In the manufacturing process of a semiconductor device or a flat panel display (FPD), a plasma is widely used in a process such as etching, deposit, oxidation, sputtering or the like since it has a good reactivity with a processing gas at a relatively low temperature. In such plasma process, the plasma is mostly generated by a radio frequency (RF) discharge in the megahertz range. Specifically, the plasma generated by the RF discharge is classified into a capacitively coupled plasma and an inductively coupled plasma.
Typically, an inductively coupled plasma processing apparatus includes a processing chamber, at least a portion (e.g., a ceiling portion) of which is formed of a dielectric window; and a coil-shaped RF antenna provided outside the dielectric window, and an RF power is supplied to the RF antenna. The processing chamber serves as a vacuum chamber capable of being depressurized, and a target substrate (e.g., a semiconductor wafer, a glass substrate or the like) to be processed is provided at a central portion of the chamber. Further, a processing gas is introduced into a processing space between the dielectric window and the substrate. As an RF current flows though the RF antenna, an RF magnetic field is generated around the RF antenna, wherein magnetic force lines of the RF magnetic field travel through the dielectric window and the processing space. The temporal alteration of the generated RF magnetic field causes an electric field to be induced azimuthally. Moreover, electrons azimuthally accelerated by the induced electric field collide with molecules and/or atoms of the processing gas, to thereby ionize the processing gas and generate a plasma in a doughnut shape.
By increasing the size of the processing space in the chamber, the plasma is efficiently diffused in all directions (especially, in the radial direction), thereby making the density of the plasma on the substrate uniform. However, the uniformity of the plasma density on the substrate that is obtained by merely using a typical RF antenna is generally insufficient for the plasma process. Accordingly, even as for the inductively coupled plasma processing apparatus, it becomes one of the most important factors to improve the uniformity of the plasma density on the substrate, since it determines the uniformity and the reproducibility of the plasma process itself and, furthermore, the manufacturing production yield. Several techniques related thereto have been so far proposed.
In a representative conventional technique for improving the uniformity of the plasma density, the RF antenna is divided into a plurality of segments. Such RF antenna dividing method includes a first method for individually supplying RF powers to the respective antenna segments (see, e.g., U.S. Pat. No. 5,401,350); and a second method for controlling the division ratio of the RF powers that are divided from one RF power supply to all the antenna segments by changing each impedance of the antenna segments in an additional circuit such as a capacitor or the like (see, e.g., U.S. Pat. No. 5,907,221).
In addition, there has been known a method in which a single RF antenna is used and a passive antenna is provided around the RF antenna (see, e.g., Japanese Patent Application Publication No. 2005-534150 (JP2005-534150A)). The passive antenna is formed of an independent coil to which an RF power is not supplied from the RF power supply. The passive antenna acts to decrease the intensity of the magnetic field in the loop of the passive antenna compared to that of the magnetic field generated by the RF antenna (inductive antenna) and increase the intensity of the magnetic field outside the loop of the passive antenna. Accordingly, the radial distribution of the RF electromagnetic field in the plasma generating region in the chamber is changed.
However, the first method of the above-described RF antenna dividing methods is disadvantageous in that the requirement for a plurality of RF power supplies and a plurality of matchers corresponding thereto makes the configuration of the RF power supply unit complex and increases the costs remarkably. The second method is rarely used due to the poor controllability. To be specific, it is difficult to control the division ratio only by the additional circuit because each of impedances of the antenna segments is affected by the impedances of the plasma as well as other antennas segments.
In the conventional method using the passive antenna described in JP2005-534150A, the magnetic field generated by the RF antenna (inductive antenna) is affected by the passive antenna and, thus, the radial distribution of the RF electromagnetic field in the plasma generation region in the chamber can be changed. Since, however, the effect of the passive antenna has not been sufficiently examined to be understood enough, it is not easy to realize the specific configuration of the apparatus for accurately controlling the plasma density distribution by using the passive antenna.
Along with the trend toward scaling-up of a substrate and scaling-down of a device, the recent trend in the current plasma process has brought about the demand for high-density plasma sources with larger diameters at a low pressure. Therefore, it is difficult to improve the uniformity of the process on the substrate.
In this regard, the inductively coupled plasma processing apparatus generates a plasma in a doughnut shape inside the dielectric window close to the RF antenna and diffuses the plasma generated in the doughnut shape in all directions toward the substrate. However, the diffusion shape of the plasma is varied depending on the pressure inside the chamber, which results in changes in the plasma density distribution on the substrate. Hence, if it is not possible to correct the magnetic field generated by the RF antenna (inductive antenna) to maintain the uniformity of the plasma density on the substrate regardless of the changes in the pressure of the process recipe, it is difficult to cope with various and high process performances required by the current plasma processing apparatus.